SCADA systems have long been used in a variety of utility markets, such as natural gas collection and distribution, power generation and distribution, water distribution, oil fields and distribution systems, etc. In general, these systems employ a number of remote terminal units (RTUs) in conjunction with various pieces of field equipment (re-closers, switches, pumps, interrupters, capacitor banks, etc.). The RTUs are essentially communication interfaces and may be integrated directly into the field equipment, or, more often, are connected to the field equipment as external communication units. The RTUs are periodically interrogated or “polled” by a central unit, and the RTUs respond with data gathered from their associated field equipment or systems. The interrogation may be specific (meaning that the central unit contacts a specific RTU using some form of unique identifier), or global (in which case the central unit sends a single poll and all of the RTUs that receive the poll respond sequentially according to some predetermined order of response).
SCADA RTUs are available from a number of vendors and have a variety of forms. In general, however, all RTUs act as communication interfaces for whatever pieces of field equipment they are associated with. A communication device (e.g., a modem or the like) connected to the RTU enables communications between the RTU and the central unit over a communications network (e.g., the PSTN other network). This presents a problem because each of these communication devices is designed to be specific in purpose. That is, each communication device is designed to be used for one particular application, for example, one particular form of communication link to/from the central unit. Thus, while some communication devices may be configured for communication over a cellular network, others may only be configured for use with leased lines or satellite communication links.
This latter point is important because having a variety of different communication mechanisms to/from the central unit of a SCADA system generally means that similar transceiver systems must be deployed both at the remote site and at the central office or other site. This leads to the undesirable situation of having a dedicated receiver for each (or at best a few) RTU/field equipment piece that is deployed. Such a communication system is both costly and difficult to maintain.
Some vendors have attempted to solve this problem by providing apparatus that integrate the RTU and the communication device. For example, the series 33XX RTUs produced by Bristol Babcock of Watertown, Conn. appear to allow a user to customize a general form of RTU for a specific application by ordering the RTU with one of a number of available communication cards. The problem with this approach of semi-custom RTUs is that one is still left with the problem of providing dedicated transceivers for each variant of communication interface. Further, each semi-custom RTU is capable of interfacing with only a specific piece of field equipment.
A further problem with many existing SCADA systems is that they do not provide a secure form of communication between the RTU and the central unit. Thus, unauthorized persons may be able to monitor or interfere with transmissions or even be able to insert unauthorized communications into the SCADA network, possibly compromising the system being monitored/controlled. Finally, current SCADA systems still require field service personnel be dispatched whenever historical information is to be retrieved from an RTU. That is, the RTU-to-central unit communication system does not support the transmission of large data files, such as history logs and the like.
What is needed therefore is an improved SCADA communication device.